1. Field of the Invention
This invention relates to an on-site wastewater treatment system and on-site method of treating wastewater.
2. Prior Art Relevant to the Disclosure
On-site disposal of wastewater (sewage) from single family residences and commercial establishments in areas with no conventional sewer system has conventionally been accomplished by a septic tank system where the anaerobic effluent discharged from the septic tank, after settling of the solids portion of the incoming wastewater, is passed into a subsurface drainfield for percolation into the surrounding soil. Such a system works satisfactorily if properly installed and if proper soil conditions for disposal of the effluent by the drainfield exist. In many areas, soil conditions are unsuitable for treatment of the effluent from septic tanks. In such areas one alternative is to utilize small treatment plants which make use of chemical and/or biological treatment means, such as primary, secondary and sometimes tertiary treatment to render the effluent suitable for disposal. Such treatment plants are prohibitively expensive, both to construct and operate unless there is a sufficiently dense population base or industrial base for financially supporting the treatment plant. Such treatment plants are generally not economically feasible for treatment of domestic sewage in rural and semi-rural areas. Other alternative methods of on-site waste treatment and disposal are known; however, many of them have never been accepted by local health authorities because of insufficient treatment of the wastewater.
Two alternative systems are illustrated by FIGS. 1 and 2 of the drawings. FIG. 1 illustrates a system known as the intermittent sand filter system. In the intermittent sand filter system anaerobic effluent from a septic tank is pumped into subsurface drains positioned in a sand filter. The effluent is generally pumped into one of the subsurface drains in one area of the filter bed for a period of time and then switched to pump it into the other subsurface drain or drains of the filter bed for a further period of time to allow regeneration of the bed around the first drain. In the intermittent sand filter, anaerobic slime builds up directly beneath the perforated drain pipes through which the effluent enters. The action of the intermittent sand filter is primarily mechanical and the bacterial count of effluent leaving the sand filter is not reduced substantially. The only oxygen which reaches the effluent in the sand filter for aerobic degradation of the fecal bacteria is that which filters down through the top layer of sand. A major disadvantage of the intermittent sand filter is the physical size of the filter required to treat a particular amount of effluent. For example, to treat 450 gallons of effluent by such an intermittent sand filter would require a sand filter accommodating two 50 foot subsurface drains.
FIG. 2 illustrates another alternative system known as the Hines-Favreau system. In the Hines-Favreau system effluent is discharged from the septic tank into a recirculating tank from where it is pumped into perforated drain troughs positioned above the level of sand in the filter bed. The effluent trickles down through the sand filter with a portion of the effluent reentering the recirculation tank and a portion being discharged to a drain field. The portion entering the recirculation tank is again recirculated through the sand filter. With the Hines-Favreau system a high degree of mechanical filtration occurs through the sand filter. Clumps of algae, however, tend to build up directly beneath where the effluent trickles down onto the surface of the sand filter. Over a period of time this causes channelization through the filter bed to occur and inefficient and ineffective treatment results. As is true of the intermittent sand filter system, the bacterial count of effluent discharged from the sand filter of the Hines-Favreau system, although lower generally than that discharged from the intermittent sand filter system, is still too high to satisfy health authorities. After a period of time with the Hines-Favreau system, the sand filter becomes matted and clogged with filtered solids and a bacteriological mat and must be cleaned and/or the sand replaced. If not, the system fails to work effectively.
In neither of the two prior art systems described is there an effective retention/displacement cycle of the effluent within the sand filter as occurs in the system claimed. Because of the high ratio of retention time to displacement which occurs in the media bed of the system described and claimed in this application, bacterial action occurs which results in substantially lower bacteria counts in the discharged effluent.